// well, this is a copy of linux kernel's vsprintf.c

#include <stdarg.h>
#include <string.h>

static int skip_atoi(const char** s) {
    int i = 0;
    while (is_digit(**s))
        i = i * 10 + *((*s)++) - '0';
    return i;
}

#define ZEROPAD	1		/* pad with zero */
#define SIGN	2		/* unsigned/signed long */
#define PLUS	4		/* show plus */
#define SPACE	8		/* space if plus */
#define LEFT	16		/* left justified */
#define SPECIAL	32		/* 0x */
#define SMALL	64		/* use 'abcdef' instead of 'ABCDEF' */

#define do_div(n,base) ({ \
int __res; \
__asm__("divl %4":"=a" (n),"=d" (__res):"0" (n),"1" (0),"r" (base)); \
__res; })

static char* number(char* str, int num, int base, int size, int precision
    , int type) {
    char c, sign, tmp[36];
    const char* digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    int i;

    if (type & SMALL) digits = "0123456789abcdefghijklmnopqrstuvwxyz";
    if (type & LEFT) type &= ~ZEROPAD;
    if (base < 2 || base>36)
        return 0;
    c = (type & ZEROPAD) ? '0' : ' ';
    if (type & SIGN && num < 0) {
        sign = '-';
        num = -num;
    } else
        sign = (type & PLUS) ? '+' : ((type & SPACE) ? ' ' : 0);
    if (sign) size--;
    if (type & SPECIAL) {
        if (base == 16) {
            size -= 2;
        } else if (base == 8) size--;
    }
    i = 0;
    if (num == 0)
        tmp[i++] = '0';
    else while (num != 0)
        tmp[i++] = digits[do_div(num, base)];
    if (i > precision) precision = i;
    size -= precision;
    if (!(type & (ZEROPAD + LEFT)))
        while (size-- > 0)
            *str++ = ' ';
    if (sign)
        *str++ = sign;
    if (type & SPECIAL) {
        if (base == 8)
            *str++ = '0';
        else if (base == 16) {
            *str++ = '0';
            *str++ = digits[33];
        }
    }
    if (!(type & LEFT))
        while (size-- > 0)
            *str++ = c;
    while (i < precision--)
        *str++ = '0';
    while (i-- > 0)
        *str++ = tmp[i];
    while (size-- > 0)
        *str++ = ' ';
    return str;
}

int vsprintf(char* buf, const char* fmt, va_list args) {
    int len;
    int i;
    char* str;
    char* s;
    int* ip;

    int flags;		/* flags to number() */

    int field_width;	/* width of output field */
    int precision;		/* min. # of digits for integers; max
                   number of chars for from string */
    int qualifier;		/* 'h', 'l', or 'L' for integer fields */

    for (str = buf; *fmt; ++fmt) {
        if (*fmt != '%') {
            *str++ = *fmt;
            continue;
        }

        /* process flags */
        flags = 0;
    repeat:
        ++fmt;		/* this also skips first '%' */
        switch (*fmt) {
        case '-': flags |= LEFT; goto repeat;
        case '+': flags |= PLUS; goto repeat;
        case ' ': flags |= SPACE; goto repeat;
        case '#': flags |= SPECIAL; goto repeat;
        case '0': flags |= ZEROPAD; goto repeat;
        }

        /* get field width */
        field_width = -1;
        if (is_digit(*fmt))
            field_width = skip_atoi(&fmt);
        else if (*fmt == '*') {
            /* it's the next argument */
            field_width = va_arg(args, int);
            if (field_width < 0) {
                field_width = -field_width;
                flags |= LEFT;
            }
        }

        /* get the precision */
        precision = -1;
        if (*fmt == '.') {
            ++fmt;
            if (is_digit(*fmt))
                precision = skip_atoi(&fmt);
            else if (*fmt == '*') {
                /* it's the next argument */
                precision = va_arg(args, int);
            }
            if (precision < 0)
                precision = 0;
        }

        /* get the conversion qualifier */
        qualifier = -1;
        if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') {
            qualifier = *fmt;
            ++fmt;
        }

        switch (*fmt) {
        case 'c':
            if (!(flags & LEFT))
                while (--field_width > 0)
                    *str++ = ' ';
            *str++ = (unsigned char)va_arg(args, int);
            while (--field_width > 0)
                *str++ = ' ';
            break;

        case 's':
            s = va_arg(args, char*);
            len = strlen(s);
            if (precision < 0)
                precision = len;
            else if (len > precision)
                len = precision;

            if (!(flags & LEFT))
                while (len < field_width--)
                    *str++ = ' ';
            for (i = 0; i < len; ++i)
                *str++ = *s++;
            while (len < field_width--)
                *str++ = ' ';
            break;

        case 'o':
            str = number(str, va_arg(args, unsigned long), 8,
                field_width, precision, flags);
            break;

        case 'p':
            if (field_width == -1) {
                field_width = 8;
                flags |= ZEROPAD;
            }
            str = number(str,
                (unsigned long)va_arg(args, void*), 16,
                field_width, precision, flags);
            break;

        case 'x':
            flags |= SMALL;
            // fall through
        case 'X':
            str = number(str, va_arg(args, unsigned long), 16,
                field_width, precision, flags);
            break;

        case 'd':
        case 'i':
            flags |= SIGN;
            // fall through
        case 'u':
            str = number(str, va_arg(args, unsigned long), 10,
                field_width, precision, flags);
            break;

        case 'n':
            ip = va_arg(args, int*);
            *ip = (str - buf);
            break;

        default:
            if (*fmt != '%')
                *str++ = '%';
            if (*fmt)
                *str++ = *fmt;
            else
                --fmt;
            break;
        }
    }
    *str = '\0';
    return str - buf;
}

int sprintf(char* resBuf, const char* fmt, ...) {
    va_list args;
    va_start(args, fmt);
    int res = vsprintf(resBuf, fmt, args);
    va_end(args);
    return res;
}